EP1817845A1 - Decodeur audio basse puissance sensible a la perception pour dispositifs portables - Google Patents

Decodeur audio basse puissance sensible a la perception pour dispositifs portables

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Publication number
EP1817845A1
EP1817845A1 EP05807683A EP05807683A EP1817845A1 EP 1817845 A1 EP1817845 A1 EP 1817845A1 EP 05807683 A EP05807683 A EP 05807683A EP 05807683 A EP05807683 A EP 05807683A EP 1817845 A1 EP1817845 A1 EP 1817845A1
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EP
European Patent Office
Prior art keywords
audio
decoding
audio data
data representing
processor
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP05807683A
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German (de)
English (en)
Other versions
EP1817845A4 (fr
Inventor
Ye c/o National University of Singapore WANG
S. National University of Singapore CHAKRABORTY
Wendong National University of Singapore HUANG
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National University of Singapore
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National University of Singapore
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Publication date
Application filed by National University of Singapore filed Critical National University of Singapore
Publication of EP1817845A1 publication Critical patent/EP1817845A1/fr
Publication of EP1817845A4 publication Critical patent/EP1817845A4/fr
Withdrawn legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • G10L—SPEECH ANALYSIS TECHNIQUES OR SPEECH SYNTHESIS; SPEECH RECOGNITION; SPEECH OR VOICE PROCESSING TECHNIQUES; SPEECH OR AUDIO CODING OR DECODING
    • G10L19/00—Speech or audio signals analysis-synthesis techniques for redundancy reduction, e.g. in vocoders; Coding or decoding of speech or audio signals, using source filter models or psychoacoustic analysis
    • G10L19/02—Speech or audio signals analysis-synthesis techniques for redundancy reduction, e.g. in vocoders; Coding or decoding of speech or audio signals, using source filter models or psychoacoustic analysis using spectral analysis, e.g. transform vocoders or subband vocoders
    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • G10L—SPEECH ANALYSIS TECHNIQUES OR SPEECH SYNTHESIS; SPEECH RECOGNITION; SPEECH OR VOICE PROCESSING TECHNIQUES; SPEECH OR AUDIO CODING OR DECODING
    • G10L19/00—Speech or audio signals analysis-synthesis techniques for redundancy reduction, e.g. in vocoders; Coding or decoding of speech or audio signals, using source filter models or psychoacoustic analysis
    • G10L19/04—Speech or audio signals analysis-synthesis techniques for redundancy reduction, e.g. in vocoders; Coding or decoding of speech or audio signals, using source filter models or psychoacoustic analysis using predictive techniques
    • G10L19/16—Vocoder architecture
    • G10L19/18—Vocoders using multiple modes
    • G10L19/24—Variable rate codecs, e.g. for generating different qualities using a scalable representation such as hierarchical encoding or layered encoding
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
    • H03M7/00—Conversion of a code where information is represented by a given sequence or number of digits to a code where the same, similar or subset of information is represented by a different sequence or number of digits
    • H03M7/30—Compression; Expansion; Suppression of unnecessary data, e.g. redundancy reduction

Definitions

  • the present invention relates generally to low-power decoding in multimedia applications and, in particular, to a method and apparatus for decoding audio data, and to
  • I a computer program product including a computer readable medium having recorded thereon a computer program for decoding audio data.
  • portable consumer electronics devices such as mobile phones, portable digital assistants (PDA) and portable audio players comprise embedded computer systems.
  • embedded computer systems are typically configured according to general-purpose computer hardware platforms or architecture templates.
  • the only difference between these consumer electronic devices is typically the software application that is being executed on the particular device.
  • several different functionalities are increasingly being clubbed into one device.
  • some mobile phones also work as portable digital assistants (PDA) and/or portable audio players.
  • PDA portable digital assistants
  • Power consumption of the computer systems embedded in the portable devices is probably the most critical constraint in the design of both, hardware and software, for such portable devices.
  • One known method of minimising power consumption of computer systems embedded in portable devices is to dynamically scale the voltage and frequency (i.e., clock frequency) of the processor of an embedded computer system in response to the variable workload involved in processing multimedia streams.
  • Another known method of minimising power consumption of computer systems embedded in portable devices uses buffers to smooth out multimedia streams and decouple two architectural components having different processing rates. This enables the embedded processor to be periodically switched off or for the processor to be run at a lower frequency, thereby saving energy.
  • QoS Quality-of-Service
  • a method of decoding audio data representing an audio clip comprising the steps of: selecting one of a predetermined number of frequency bands; decoding a portion of the audio data representing said audio clip according to the selected frequency band, wherein a remaining portion of the audio data representing said audio clip is discarded; and converting the decoded portion of audio data into sample data representing the decoded audio data.
  • a decoder for decoding audio data representing an audio clip, said method comprising the steps of: decoding level selection means for selecting one of a predetermined number of frequency bands; decoding means for decoding a portion of the audio data representing said audio clip according to the selected frequency band, wherein a remaining portion of the audio data representing said audio clip is discarded; and data conversion means for converting the decoded portion of audio data into sample data representing the decoded audio data.
  • a portable electronic device comprising: decoding level selection means for selecting one of a predetermined number of frequency bands; decoding means for decoding a portion of audio data representing an audio clip according to the selected frequency band, wherein a remaining portion of the audio data representing said audio clip is discarded; and data conversion means for converting the decoded portion of audio data into sample data representing the decoded audio data.
  • Fig. 1 is a schematic block diagram of a portable computing device comprising a processor, upon which embodiments described can be practiced;
  • Fig. 2 shows the processor of Fig. 1 taking a coded bitstream as input and producing a stream of decoded pulse code modulated (PCM) samples;
  • Fig. 3 shows the frame structure of an MPEG 1, Layer 3 (i.e., MP3) standard bitstream;
  • Fig. 4 is a block diagram showing the modules of a standard MP3 decoder together with the proposed new decoder architecture
  • Fig. 5 shows an internal buffer and playout buffer used by the processor of Fig. 1 in decoding audio data
  • - A - Fig. 6 is a graph showing the cycle requirement for the processor of Fig. 1 per granule, corresponding to an audio clip, for a predetermined duration
  • Fig. 7 shows the processor cycles required within any interval of length t corresponding to the decoding levels of the preferred embodiment; and Fig. 8 shows a method of decoding audio data in the form of a coded bit stream, in accordance with the preferred embodiment.
  • perceptual audio coder/decoders i.e., codecs
  • codecs are designed to achieve transparent audio quality at least at high bit rates.
  • the frequency range of a high quality audio codec such as MP3 is up to about 20 kHz.
  • most adults, particularly older ones can hardly hear frequency components above 16 kHz. Therefore, it is unnecessary to determine the perceptually irrelevant frequency components.
  • some bands register more loudly than others. In general, the high frequency bands are perceptually less important than the low frequency bands. There is little perceptual degradation if some high frequency components are left un-decoded.
  • a standard decoder such as an MP3 decoder will simply decode everything in an input bit stream without considering the hearing ability of individual users with or without hearing loss. This results in a significant amount of irrelevant computation, thereby wasting battery power of a portable computing device or the like using such a decoder.
  • a method 800 of decoding audio data in the form of a coded bit stream, in accordance with the preferred embodiment, is described below with reference to Figs. 1 to 8.
  • the principles of the preferred method 800 described herein have general applicability to most existing audio formats. However, for ease of explanation, the steps of the preferred method 800 are described with reference to the MPEG 1, Layer 3 audio format, also known as MP3, audio format.
  • MP3 is a non-scalable codec and has widespread popularity.
  • the method 800 is particularly applicable to non-scalable codecs like MP3 and also Advanced Audio Coding (AAC).
  • Non-scalable codecs incur a lower workload and are more popular than scalable codecs, such as an MPEG-4 scalable codec, where only a base layer is typically decoded with an enhancement layer being ignored.
  • the method 800 integrates an individual user's own judgment on the desired audio quality allowing a user to switch between multiple output quality levels. Each such level is associated with a different level of power consumption, and hence battery lifetime.
  • the described method 800 is perception-aware, in the sense that the difference in the perceived output quality associated with the different levels is relatively small. But decoding the same audio data, such as an audio clip in the form of a coded bit stream, at a lower output quality level leads to significant savings in the energy consumed by the processor embedded in a portable device.
  • the method 800 allows the user to choose an appropriate decoding profile suitable for the particular service and signal type also prolonging the battery life of a portable computing device using the method 800.
  • the method 800 allows users to control the tradeoff between the battery life and the decoded audio quality, with the knowledge that slightly degraded audio quality (this degradation may not even be perceptible to the particular user) can significantly increase the battery life of a portable audio player, for example.
  • This feature allows the user to tailor the acceptable quality level of the decoded audio according to their hearing ability, listening environment and service type. For example, in a quiet environment the user may prefer perfect sound quality with more power consumption. On the other hand, the user might prefer a longer battery life with slightly degraded audio quality during a long haul flight.
  • the method 800 is preferably practiced using a battery-powered portable computing device 100 (e.g., a portable audio (or multi-media) player, a mobile (multi-media) telephone, a PDA or the like) such as that shown in Fig. 1.
  • a battery-powered portable computing device 100 e.g., a portable audio (or multi-media) player, a mobile (multi-media) telephone, a PDA or the like
  • the processes of Figs. 2 to 8 may be implemented as software, such as a software program executing within the portable computing device 100.
  • the steps of the method 800 are effected by instructions in the software that are carried out by the portable computing device 100.
  • the instructions may be formed as one or more software modules, each for performing one or more particular tasks.
  • the software may also be divided into two separate parts, in
  • the software may be stored in a computer readable medium, including the storage devices described below, for example.
  • the software may be loaded into the portable computing device 100 by a manufacturer, for example, from
  • a computer readable medium having such software or computer
  • program recorded on it is a computer program product.
  • the use of the computer program product in the computer system 100 preferably effects an advantageous apparatus for implementing the described method 800.
  • the portable computing device 100 includes at least one processor unit 105, and a memory unit 106, for example formed from semiconductor random access memory (RAM) and read only memory (ROM).
  • the portable computing device 100 may also comprise a keypad 102, a display 114 such as a liquid crystal display (LCD), a speaker 117 and a microphone 113.
  • the portable computing device 100 is preferably powered by
  • a transceiver device 116 is used by the portable computing device 100 for
  • a communications network 120 e.g., the telecommunications
  • the components 105 to 1 17 of the portable computing device 100 are configured to be connectable via a wireless communications channel 121 or other functional medium.
  • the components 105 to 1 17 of the portable computing device 100 are configured to be connectable via a wireless communications channel 121 or other functional medium.
  • the application program is resident in ROM of the memory device 106
  • the term "computer readable medium” as used herein refers to any storage or transmission medium that participates in providing instructions and/or data to the portable computing device 100 for execution and/or processing.
  • the method 800 may alternatively be implemented in dedicated hardware unit comprising one or more integrated circuits performing the functions or sub functions of the described method.
  • a decoding level selected by a user to decode any audio clip determines the frequency with which the processor 105 is to be executed.
  • the method 800 does not involve any runtime scaling of the processor 105 voltage or frequency. If the processor 105 has a fixed number of voltage-frequency operating points, the decoding levels in the method 800 may be tuned to match these operating points.
  • the frequency bandwidth of the portable computing device 100 comprising an audio decoder (e.g., an MP3 decoder) implemented therein is partitioned into a number of groups that is equal to the number of decoding levels. These groups are preferably ordered according to their perceptual relevance, which will be described in detail below. If there are four levels of decoding (i.e. Levels 1—4) then the frequency bandwidth group that has the highest perceptual relevance may be associated with Level 1 and the group that has the lowest perceptual relevance may be associated with Level 4.
  • Levels 1 Such a partitioning of the frequency bandwidth into four levels in the case of MP3 is shown in Table 1 below. Column 2 of Table 1 (i.e., Decoded subband index) is described below.
  • the processor 105 implementing the steps of the method 800 may be referred to as a "Perception-aware Low-power MP3 (PL-MP3)" decoder.
  • the method 800 is not only useful with general-purpose voltage and frequency scalable processors, but also with general-purpose processors without voltage and frequency scalability.
  • the method 800 may also be used with a processor that does not allow frequency scaling and is not powerful enough to do full MP3 decoding. In this instance, the method 800 may be used to decode regular MP3 files at a relative lower quality.
  • the method 800 allows a user to choose a decoding level (i.e., one of four such levels) depending on processing power supplied by the processor 105.
  • the method 800 is executed by the processor 105 based on the decoding level selected by the user. Each level is associated with a different level of power consumption and a corresponding output audio quality level.
  • the processor 105 takes audio data in the form of a coded bit stream as input and produces a stream of decoded data in the form of pulse code modulated (PCM) samples, as seen in Fig. 2.
  • PCM pulse code modulated
  • the method 800 may be applied to decode a coded bit stream that is being downloaded or streamed from a network.
  • the method 800 may also be used to decode an audio clip in the form of a coded bit stream stored within the memory 106, for example, of the portable computing device 100.
  • the method 800 lowers the power consumption of the processor 105 executing the software implementing the steps of the method 800.
  • the method 800 does not rely on any specific hardware implementations or on any co-processors to implement specific parts of the decoder.
  • the method 800 is very useful for use with PDAs, portable audio players or mobile phones and the like comprising powerful voltage and frequency scalable processors, which may all be used as portable audio/video players.
  • the MP3 bitstream has a frame structure, as seen in Fig. 3.
  • a frame 300 of the MP3 bitstream contains a header 301, an optional CRC 302 for error protection, a set of control bits coded as side information 303, followed by the main data 304 consisting of two granules (i.e., Granule 0 and Granule 2) which are the basic coding units in MP3.
  • each granule e.g., Granule 1
  • contains data for two channels which consists of scale factors 305 and Huffman coded spectral data 306. It is also possible to have some ancillary data inserted at the end of each frame.
  • the method 800 processes such an MP3 bit stream frame by frame or granule by granule.
  • the method 800 of decoding audio data will now be described with reference to Fig. 8.
  • the method 800 may be implemented as software resident in the ROM 106 and being controlled in its execution by the processor 105.
  • the portable computing device 100 implementing the method 800 may be configured in accordance with a standard MP3 audio decoder 400 as seen in Fig. 4.
  • Each of the steps of the method 800 may be implemented using separate software modules.
  • the method 800 begins at the first step 801, where the one of the four decoding levels (i.e., Levels 1 - 4) of Table 1 are selected.
  • the user of the portable computing device 100 may select one of the four decoding levels using the keypad 102.
  • the processor 105 may store a flag in the RAM of the memory 106 indicating which one of the four decoding levels has been selected.
  • the processor 105 parses data in the form of a coded input bit stream and stores the data in an internal buffer 500 (see Fig. 5) configured within the memory 106.
  • the internal buffer 500 will be described in more detail below.
  • the processor 105 decodes the side information of the stored data using Huffman decoding.
  • Step 803 may be performed using a software module such as the Huffman decoding software module 401 of the standard MP3 decoder 400, as seen in Fig. 4.
  • the method 800 continues at the next step 804, where the processor 105 converts a frequency band of the decoded audio data into PCM audio samples, according to the decoding level selected at step 801.
  • Step 804 may be performed by software modules such as the dequantization software module 402, the inverse modified discrete cosine transform (IMDCT) software module 403 and the polyphase synthesis software module 404 of the standard MP3 decoder 400 as seen in Fig. 4.
  • the dequantization software module 402 the inverse modified discrete cosine transform (IMDCT) software module 403 and the polyphase synthesis software module 404 of the standard MP3 decoder 400 as seen in Fig. 4.
  • IMDCT inverse modified discrete cosine transform
  • the method 800 concludes at the next step 805, where the processor 105 writes the PCM audio samples into a playout buffer 501 (see Fig. 5) configured within memory 106.
  • This playout buffer 501 may then be read by the processor 105 at some specified rate and be output as audio via the speakers 117.
  • the three modules of a standard MP3 decoder 400 which incur the highest workload are the de-quantization module 402, the IMDCT module 403 and the polyphase synthesis filterbank module 404.
  • the standard MP3 decoder 400 decodes the entire frequency band, which corresponds to the highest computational workload. As seen in Fig.
  • the de-quantization module 402 processes only a partial frequency range and thereby incur less computational cost.
  • the Do Not Zero-Pute algorithm tries to optimize the polyphase filterbank computation in the MPEG 1 layer II by eliminating costly computing cycles being wasted at processing useless zero-valued data.
  • the present inventors classify this kind of approach as eliminating redundant computation, hi contrast, the method 800 partitions the workload according to frequency bands with different perceptual relevance and allows the user to eliminate the irrelevant computation.
  • Equation (1) The computation required to be performed by the processor 105 for the de- quantization of a granule (in the case of long blocks) is expressed as Equation (1) as follows: 1 x ⁇ ⁇ signyis,)* «,• 3
  • global_gain is the logarithmical quantizer step size for the entire granule gr.
  • Scalefac_multiplier is the multiplier for scale factorbands.
  • Scalefac_l is the logarithmically quantized factor for scale factorband sfb of channel ch of granule gr.
  • Preflag is the flag for additional high frequency amplification of the quantized values.
  • Pretab is the preemphasis table for scale factorbands. xr,is the i-th dequantized
  • the computation required for the IMDCT module 403 may be expressed in accordance with Equation (2) as follows:
  • Equation (3) Equation (4) as follows:
  • V 1 ⁇ S k cos(; ⁇ (2A: + lX «/2 + i)l2n) (4)
  • Equation (4) shows the computational workload of the processor 105 implementing the method 800 decreases linearly with the bandwidth.
  • step 802 i.e., as performed by the Huffman decoding module 401
  • the workload associated with the subsequent step 804 i.e., as performed by the modules 402, 403 and 404
  • a granularity may be selected that corresponds to all the 32 subbands defined in the MPEG 1 audio standard.
  • these 32 subbands are partitioned into only four groups, where each group corresponds to a decoding level, as seen in Fig. 4 and Table 1.
  • the decoding Level 1 covers the lowest frequency bandwidth (0 - 5.5 kHz) which may be defined as the base layer. Although the base layer occupies only a quarter of the total bandwidth and contributes to roughly a quarter of the total computational workload performed by the processor 105 in decoding an audio clip, the base layer is perceptually the most relevant frequency band.
  • the output audio quality corresponding to Level 1 of Table 1 is certainly sufficient for services like news and sports commentary.
  • Level 2 covers a bandwidth of 11 kHz and almost reaches the FM radio quality, which is sufficiently good even for listening to music clips, especially in noisy environments.
  • Level 3 covers a bandwidth of 16.5 kHz and produces an output that is very close to CD quality.
  • Level 4 corresponds to the standard MP3 decoder, which decodes the full bandwidth of 22 kHz.
  • Levels 1 , 2 and 3 process only a part of the data representing the different frequency
  • Level 4 processes all the data and is therefore computationally more
  • the minimum operating frequency of the processor 105 for decoding audio data in
  • the computed frequency can then be used to estimate the power consumption due to the processor 105.
  • the variability in the number of bits constituting a granule and also the variability in the processor cycle requirement in processing any granule is taken into account. By accounting for this variability, the change in processor 105 frequency requirement when the playback delay of the portable computing device 100 is changed may be determined.
  • the processor 105 uses the internal buffer
  • 500 of size b configured within memory 106, in decoding audio data in the form of an
  • the decoded audio stream which is a sequence of
  • This playout buffer 501 is read by the processor 105 at some specified rate. Assuming that the input bitstream to be decoded is fed into the internal buffer 500 at a constant rate of r bits/sec.
  • the number of bits constituting a granule in the MP3 frame structure is variable. The maximum number of bits per granule can almost be three times the minimum number of bits in a granule, where this minimum number is around 1200
  • ⁇ '(k) denotes the minimum number of bits constituting any k consecutive granules in an
  • ⁇ u (k) can be obtained by analyzing a number of audio clips that are representative of
  • x(t) denote the number of granules arriving in the internal buffer 501 over the time interval [0, t]. Because of the variability in the number of bits constituting a granule, the function x(t) will be audio clip dependent.
  • a 1 (A) denotes the minimum number of granules that can arrive in the internal
  • ⁇ '( ⁇ ) may be defined as
  • this variability may be captured using two functions ⁇ 1 (Jc) and ⁇ " (k) . Both the
  • FIG. 6 shows the processor cycle requirement corresponding to the four decoding levels of Table 1. There are two points to be noted in Fig. 6: (i) the increasing processor cycle requirement as the decoding level is increased, (ii) the variability of the processor cycle requirement per granule for any decoding level.
  • the playout buffer 501 is readout by the processor 105 at a constant rate of c PCM samples/sec, after a playback delay (or buffering time) of d seconds.
  • c is equal to 44.1K PCM samples/sec for each channel (and therefore, 44.1K x 2 PCM samples/sec for stereo output) and d can be set to a value between 0.5 to 2 seconds.
  • the playout rate is equal to c/s granules/second. If the function C(t) denotes the number of granules readout by the processor 105 over the time interval [0, t], then,
  • the minimum processor frequency f to sustain the playout rate of c PCM samples/sec may be determined. This is equivalent to requiring that the playout buffer 501 never underflows. If y(t) denotes the total number of granules written into the playout buffer 501 over the time interval [0, t], then this is equivalent to requiring that y(t) > C(t) for all t> 0.
  • ⁇ (A) represents the minimum number of granules that
  • ⁇ (t) is defined in terms of the number of granules that need to be processed within any time interval of length t.
  • duration t is proportional to f 3 t , assuming a voltage and frequency scalable processor
  • the voltage is proportional to the clock frequency
  • Fig. 7 shows the processor cycles required within any interval of length t corresponding to the decoding levels of Table 1. From Fig. 7, it can be seen that each decoding level is associated with a minimum (constant) frequency / As the decoding level is increased, the associated value of f also increases.
  • Supposing the processor 105 is run at a constant frequency equal to f processor cycles/sec, corresponding to some decoding level.
  • the minimum number of granules that are guaranteed to be processed within any time interval of length ⁇ , when the processor 105 is run at a frequency f, is equal to ,,-i
  • interval of length ⁇ is given by / (fA) . It is possible to show that arrival process of
  • samples are ⁇ " (b) and sB respectively.
  • the processor 105 may be an Intel XScale 400MHz processor with the decoding levels being set according to Table 2 below.
  • the aforementioned preferred method(s) comprise a particular control flow. There are many other variants of the preferred method(s) which use different control flows without departing the spirit or scope of the invention. Furthermore one or more of the steps of the preferred method(s) may be performed in parallel rather sequentially.

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Human Computer Interaction (AREA)
  • Signal Processing (AREA)
  • Health & Medical Sciences (AREA)
  • Audiology, Speech & Language Pathology (AREA)
  • Computational Linguistics (AREA)
  • Acoustics & Sound (AREA)
  • Multimedia (AREA)
  • Quality & Reliability (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • Theoretical Computer Science (AREA)
  • Compression, Expansion, Code Conversion, And Decoders (AREA)

Abstract

Un procédé de décodage de données audio représentant une séquence audio, le procédé consistant à sélectionner une bande de fréquences parmi plusieurs bandes de fréquences définies, puis à décoder une partie des données audio représentant ladite séquence audio en fonction de la bande de fréquences choisie, ce qui fait qu'une partie restante des données audio représentant ladite séquence audio est éliminée, et enfin à convertir la partie décodée des données audio en données échantillon représentant les données audio décodées.
EP05807683A 2004-11-29 2005-11-28 Decodeur audio basse puissance sensible a la perception pour dispositifs portables Withdrawn EP1817845A4 (fr)

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PCT/SG2005/000405 WO2006057626A1 (fr) 2004-11-29 2005-11-28 Decodeur audio basse puissance sensible a la perception pour dispositifs portables

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EP2306456A1 (fr) * 2009-09-04 2011-04-06 Thomson Licensing Procédé pour le décodage d'un signal audio comportant une couche de base et une couche d'amélioration
CN101968771B (zh) * 2010-09-16 2012-05-23 北京航空航天大学 一种在dsp上实现先进音频编码算法的内存优化方法
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US7945448B2 (en) 2011-05-17
US20070299672A1 (en) 2007-12-27
KR20070093062A (ko) 2007-09-17
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CN101111997B (zh) 2012-09-05
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